Semiconductor Die Pad Through-Holes for Epoxy Adhesion
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Solution Overview
Problem
Delamination between the semiconductor die and the die pad in packaged semiconductor devices, particularly in 'no lead' packages like QFN and QFP, is a concern due to the lower adhesion of metal-loaded epoxy, which is used for high thermal conductance, increasing the risk of device failure.
Innovation Solution
A leadframe with a die pad having regions of reduced thickness and through-holes, where the epoxy fills and extends laterally beyond the through-holes, forming a plug or nail that enhances adhesion and reduces delamination risk, while maintaining high thermal conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If metal-loaded epoxy is used to achieve high thermal conductance, then thermal conductivity is improved, but adhesion to the die pad deteriorates
Solution Approach 1:
The patent applies local quality by creating regions of reduced thickness in the die pad at specific locations. These localized modifications allow the epoxy to form protrusions that extend beyond the die pad surface in certain areas while maintaining the original die pad structure elsewhere. This enables improved adhesion through geometric interlocking without compromising the overall thermal conductivity provided by the metal-loaded epoxy material.
Solution Approach 2:
The patent transitions from a two-dimensional adhesion problem (surface bonding) to a three-dimensional solution by creating protrusions that extend vertically beyond the die pad surface. The epoxy forms nails or plugs that protrude from the die pad in the vertical dimension, creating mechanical interlocking that supplements the chemical adhesion and maintains bond strength despite using metal-loaded epoxy with lower adhesion properties.
2Reliability
If the die pad surface is roughened to improve adhesion, then adhesion is improved, but manufacturing cost increases
Solution Approach 1:
The patent changes the geometric parameters of the die pad by creating regions of reduced thickness through etching or milling. This dimensional modification is achieved through standard PCB fabrication processes, avoiding the need for additional surface roughening steps. The parameter change creates mechanical interlocking features that improve adhesion without requiring costly surface treatment processes.
3Reliability
If regions of reduced thickness are created in the die pad, then adhesion is improved through epoxy protrusions, but die pad strength may be compromised
Solution Approach 1:
The patent applies segmentation by dividing the die pad into multiple regions with different thicknesses. The reduced thickness regions are strategically placed at specific locations where epoxy protrusions are desired, while the majority of the die pad maintains its full original thickness. This segmentation allows local adhesion enhancement without compromising the overall structural strength of the die pad, as the bulk material remains intact.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively reduces the risk of delamination and improves adhesion between the semiconductor die and the die pad, maintaining high thermal conductivity and reducing manufacturing costs compared to surface roughening methods.
Implementation Method 1
By extending laterally beyond the through-hole, the epoxy forms a plug or nail with a head. The head of the epoxy plug or nail may lock the epoxy layer to the die pad, thereby reducing the risk of delamination and improving the adhesion between the parts.
Implementation Method 2
For applications in which a high thermal conductance is required through the epoxy in order to conduct away heat from the chip, it is known to use metal-loaded epoxy—that is to say epoxy which has metal particles embedded in the epoxy matrix. By appropriate choice of metal—typically silver—such metal-loaded epoxy can provide a high thermal conductivity relative to other types of epoxy.
Data Source
AI summary
There is disclosed a packaged semiconductor device comprising: a leadframe having a first thickness; the leadframe comprising a die pad; a semiconductor die thereabove; and epoxy therebetween and arranged to bond the semiconductor die to the die pad; wherein in at least one region under the semiconductor die, the die pad has a second thickness less than the first thickness; wherein the die pad has at least one through-hole in the at least one region; and wherein the epoxy fills the at least one through-hole and extends thereunder and laterally beyond the through-hole. Corresponding leadframes, and an associated method of manufacture are also disclosed.